/Engine/Source/Runtime/Engine/Classes/Engine/SkeletalMesh.h
Get the Versions of the geo and skinning data. We use those versions to answer to IsLODImportedDataBuildAvailable function.
void GetLODImportedDataVersions ( const int32 LODIndex, ESkeletalMeshGeoImportVersions & OutGeoImportVersion, ESkeletalMeshSkinningImportVersions & OutSkinningImportVersion ) const